Metalaxyl and Efosite Aluminum for Control of Phytophthora Gummosis and Root Rot on Citrus

Abstract

A soil drench or stem paint of metalaxyl and efosite aluminum controlled Phytophthora gummosis of sweet orange (C. sinensis) seedlings. Applied as soil drench before inoculation with Phytophthora, metalaxyl at 50 mg/l reduced the size of stem lesions caused by P. parasitica and P. citrophthora by 64 and 79%, respectively. Soil drench treatment with efosite Al at 3000 mg/l resulted in 58 and 96% reduction of the lesion size with P. parasitica and P. citrophthora, respectively. Applied as a stem paint after stem inoculation with Phytophthora, metalaxyl at 60 g/l reduced lesion size by 51 and 52%, and efosite Al at 300 g/l reduced lesion size by 32 and 91%, with P. parasitica and P. citrophthora, respectively. Under field conditions, when applied as stem paint at 60 g/l metalaxyl reduced by 88% the size of lesions caused by P. citrophthora on lemon trees (C. limon). Root rot incidence was also reduced in sweet orange seedlings treated by a soil drench of metalaxyl at 50 mg/l but not of efosite Al at 3000 mg/l. The percentage of healthy roots, number of healthy root tips, and root weight were greater in seedlings treated with metalaxyl than in untreated seedlings grown in infested soil. Phytophthora was not detected in soil or roots from plants treated with metalaxyl but was recovered from those treated with efosite Al.